Inadequate defences and "high-level complacency" led to a devastating Taliban attack on Camp Bastion, the giant joint US/UK base in Afghanistan, which left two US marines dead and 17 UK and American personnel injured, according to a damning report by MPs.

Only 11 of 24 guard towers at the base in Helmand province were manned when 15 heavily armed Taliban insurgents infiltrated the camp and attacked the airfield on 14 September 2012. The incident also led to the destruction of six US Harrier jets. US and British troops killed 14 of the Taliban attackers and wounded the remaining one, who was detained and interrogated.

The report, by the Commons cross-party defence committee, describes the attitude of the Ministry of Defence when the MPs tried to establish the facts surrounding the attack as "obstructive and unhelpful". "The MoD were wrong to refuse to share the report on the attack prepared by Lieutenant General [Adrian] Bradshaw, in his capacity as deputy commander ISAF [the Nato-led international force in Afghanistan]", the report says. "As this was the highest-level UK report into the attack, its status as an ISAF document should not have prevented its release to us."

The committee says it was "unimpressed" by the evidence from the chief of joint operations, Lt Gen David Capewell, who explained that the number of security incidents was unusually high in Helmand Province in 2012 and that the focus of commanders had been on security incidents elsewhere in Helmand. "Unfortunately, the MoD has declined to provide the committee with comparable details of the level of security incidents recorded in Helmand for previous years as this information was classified, preventing the committee from making an informed assessment of the relative threat levels in the area at the time," Wednesday's report says.

Capewell described the decision to allow poppy cultivation close to the perimeter fence as a "minor tactical error" which had contributed to what the MPs describe as a "devastating" and "extraordinary" Taliban attack.

Though the US was ultimately responsible for protecting Camp Bastion at the time – and two US marine generals were fired as the result of the attack – "British commanders must bear a degree of responsibility for these systemic failures and associated reputational damage", the defence committee's report said.